Why was the Nasi of Naftoli called 'Achira ben Einan' (with such negative connotations), and of Dan, 'Achi'ezer ben Amishadai'?
Hadar Zekeinim (in Pasuk 18): The Cloud expelled the tribe of Dan because they had the Pesel (image of) of Michah. So Dan asked his brother Naftoli to beg for mercy on his behalf - to be an Ach (a brother) for Ezra (help) - that he (Dan) should be a Ben with Keil Shakai. And Naftoli responded with a Tefilah that 'Achira ben Einan My evil brother, who possesses idolatry, should be inside the cloud'.
Moshav Zekeinim (citing R. Yehudah ha'Chasid): When the cloud expelled Sheivet Dan 1 , Moshe and Yisrael, reealizing that there must be a reason, searched for idolatry among them. But the sinners in Dan shrewdly buried it in the ground. Naftoli then declared 'My brother (Achi), whom you called wicked (Ra) is fit to enter within the Cloud (ben Einan) 2 since we do not know the reason that he was expelled. To which B'nei Dan responded 'My brother has helped me (Achi Ezer). I and my nation - tribe (Ami) are sons of G-d Almighty (ben Shakai).